The present invention relates to a process for preparing 1,4-bishydroxyethylpiperazine (BHEPIP) of the formula I

1,4-Bis(2-hydroxyethyl)piperazine I can be used for the preparation of pharmaceuticals (cf., for example, DE 2706826 A), of surfactants, as catalyst for the production of polyurethanes (cf., for example, JP 62145076 A, Kao Corp.) and as starting compound for the preparation of diazabicyclo[2.2.2]octane (DABCO) (cf., for example, U.S. Pat. No. 3,166,558 (1965), Air Products and Chem.).
1,4-Bishydroxyethylpiperazine I was prepared for the first time by reacting piperazine (PIP) with 2-chloroethanol (J. Chem. Soc. 93, page 1802 (1908)) and later also from piperazine and ethylene oxide (DE 1 954 546 A (1971), BASF AG).
Later studies showed that BHEPIP (I) can be prepared not only from piperazine but also from diethanolamine (DEOA). Diethanolamine is formed as by-product in the preparation of ethanolamine from ethylene oxide and ammonia.
Thus, BHEPIP (I) can be obtained by heating diethanolamine in the presence of monocarboxylic or dicarboxylic acids (DE 917 784 (1954), Henkel & Cie GmbH). In example 1 of DE 917 784, a mixture of diethanolamine and glacial acetic acid (molar ratio=1:0.1) was heated at 200° C. for 20 hours while stirring and passing nitrogen through the mixture and condensing water of reaction. The yield of I was 70%.
It is known from J. Am. Chem. Soc. 61, 532 (1939) that solutions of diethanolamine in dioxane can be subjected in the presence of copper chromite catalysts to a thermal treatment at from 250 to 275° C. However, the yields of BHEPIP (I) achieved under hydrogenating conditions are no higher than 50% (cf. DE 941 909 (1956), Henkel & Cie GmbH; page 2, column 1, line 26 to column 2, line 1).
The low yield of BHEPIP (I) when using copper chromite could be increased to 68% by use of catalysts comprising 48% of copper oxide, 47% of chromium oxide, 2.5% of manganese(IV) oxide and 2.5% of barium oxide (JP 62145076 A, (1987), Kao Corp) (there, example 1). The catalyst was used in suspension in the presence of a solvent.
A disadvantage of the use of the copper catalysts mentioned is the toxicity of the catalyst constituent chromium. A high level of safety precautions therefore has to be undertaken in the separation, regeneration and/or disposal of these catalysts.
The earlier EP applications having the numbers 10166017.3 of Jun. 15, 2010 and 10187557.3 of Oct. 14, 2010 (both BASF SE) concern processes for preparing a cyclic tertiary amine of the formula I
where A is a C4-alkylene group, a C5-alkylene group or a —(CH2)2—B—(CH2)2— group, where B is oxygen (O) or an N—R1 radical and R1 is C1-C5-alkyl, aryl or C5-C7-cycloalkyl, and the radical R2 is methyl or linear or branched C2-C16-alkyl, C5-C7-cycloalkyl or C7-C20-aralkyl.